• B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.USP35

ASSAY

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• Procedure

Solution A: 0.77 g/L of ammonium acetate in water

Mobile phase: Methanol and Solution A (25:75)

Standard stock solution: 0.2 mg/mL of USP Mercaptopurine RS in the mixture of methanol and water (1:1). Transfer USP Mercaptopurine RS into a suitable volumetric flask, and add methanol equivalent to 50% of the final volume. Shake mechanically to dissolve, and dilute with water to volume.

Sample stock solution: Transfer 25 mg of Mercaptopurine into a 50-mL volumetric flask. Add 25 mL of methanol, shake mechanically for at least 45 min, and dilute with water to volume. Transfer 20 mL of this solution into a 25-mL volumetric flask, and dilute with Mobile phase to volume.

Standard stock solution A: Use the Standard stock solution from the Assay.

Standard stock solution B: 0.026 mg/mL of USP Didanosine Related Compound A RS in a mixture of methanol and water (1:1). Transfer USP Didanosine Related Compound A RS into a suitable volumetric flask, and add methanol equivalent to 50% of the final volume. Shake mechanically to dissolve, and dilute with water to volume.

Sample solution: Transfer 20 mg of Mercaptopurine into a 50-mL volumetric flask. Add 12.5 mL of methanol, shake mechanically to dissolve, and dilute with water to volume. [NoteInject the Sample solution within 1 h of preparation. ]

Sample solution: Digest 200 mg with 2 mL of 15 N sulfuric acid in a large test tube, periodically adding nitric acid, dropwise and with caution. Continue heating until practically all of the liquid has evaporated and the residue is colorless. Transfer the residue, with the aid of small portions of water, to a 25-mL volumetric flask. Add 1 mL of 15 N sulfuric acid, 0.5 mL of nitric acid, 0.75 mL of ammonium molybdate TS, and 1 mL of aminonaphtholsulfonic acid TS, then dilute with water to volume. Allow to stand for 5 min.

Blank: Add 2 mL of 15 N sulfuric acid to a large test tube, periodically adding nitric acid, dropwise and with caution. Continue heating until practically all of the liquid has evaporated and the residue is colorless. Transfer the residue, with the aid of small portions of water, to a 25-mL volumetric flask, add 1 mL of 15 N sulfuric acid, 0.5 mL of nitric acid, 0.75 mL of ammonium molybdate TS, and 1 mL of aminonaphtholsulfonic acid TS, then dilute with water to volume. Allow to stand for 5 min.